Drilling fluid contamination determination for downhole fluid sampling tool

1. A method for determining fluid contamination, comprising: obtaining a fluid sample, wherein the fluid sample comprises a reservoir fluid contaminated with a well fluid; obtaining input parameters, wherein the input parameters comprise fluid properties obtained from measurement of the fluid sample and mud filtrate composition; obtaining initial values of iterative parameters, wherein the iterative parameters comprise fluid contamination of the fluid sample; determining component mole fractions of the reservoir fluid using the initial values of the iterative parameters in a mole fraction distribution function; determining calculated fluid properties of the reservoir fluid using equation of state flash calculating; and repeating steps of determining component mole fractions and determining calculated fluid properties and further obtaining updated values of the iterative parameters for use in the mole fraction distribution function until a comparison of one or more of the calculated fluid properties with one or more of the input parameters is within a tolerance error.

2. The method of claim 1 , wherein the well fluid comprises a drilling fluid.

3. The method of claim 1 , wherein obtaining the fluid sample comprising operating a downhole fluid sampling tool in a wellbore to obtain the fluid sample.

4. The method of claim 1 , wherein the fluid properties of the input parameters comprise a component concentration, an oil density, weight % of components, bubble point pressure and a gas-to-oil ratio.

5. The method of claim 1 , wherein the iterative parameters further comprise molecular weight of C6+ components and density of C36+ components of the reservoir fluid.

6. The method of claim 1 , wherein the component mole fractions determined using the mole fraction distribution function are delumped component mole fractions of a lumped component concentration obtained in the step of analyzing the fluid sample.

7. The method of claim 1 , wherein the mole fraction distribution function is represented by the following equation: z i = { σ ⁢ ⁢ e - τ 1 ⁡ ( k - i ) α 1 , i = 5 , … ⁢ , k σ ⁢ ⁢ e - τ 2 ⁡ ( i - k ) α 2 , i = k , … ⁢ , 200 wherein i is single carbon number, z is mole fraction of component with single carbon number i, k is single carbon number with local maximum mole fraction, and σ 1 , σ 2 , τ 1 , τ 2 , and α are unknown parameters to be solved.

8. The method of claim 1 , wherein the step of determining component mole fractions of the reservoir fluid comprises solving the mole fraction distribution function for one or more unknown parameters, determining the component mole fractions of the reservoir fluid based on the mole fraction distribution function; and determining a composition of the fluid sample based at least on the component mole fractions of the reservoir fluid.

9. The method of claim 1 , wherein the comparison of one or more of the calculated fluid properties with one or more of the input parameters comprises calculated properties of gas-to-oil ratio, bubble point pressure and dead oil density with input parameters of gas-to-oil ratio, bubble point pressure and dead oil density.

10. A system for determining fluid contamination, comprising: a downhole fluid sampling tool operable to obtain fluid samples of a reservoir fluid contaminated with a well fluid while the downhole fluid sampling tool is disposed in a wellbore; and a processing unit operable to (i) obtain input parameters, wherein the input parameters comprise fluid properties obtained from measurement of the fluid sample and a mud filtrate composition; (ii) obtain initial values of iterative parameters, wherein the iterative parameters comprise fluid contamination of fluid sample; (iii) determine component mole fractions of the reservoir fluid using the initial values of the iterative parameters in a mole fraction distribution function; (iv) determine calculated fluid properties of the reservoir fluid using equation of state flash calculating; and (v) repeatedly determine component mole fractions and determining calculated fluid properties and further obtain updated values of the iterative parameters for use in the mole fraction distribution function until a comparison of one or more of the calculated fluid properties with one or more of the input parameters is within a tolerance error.

11. The system of claim 10 , wherein the downhole fluid sampling tool comprises an elongated tool body and a sensor.

12. The system of claim 10 , wherein the downhole fluid sampling tool is disposed on a distal end of a drill string.

13. The system of claim 10 , wherein the processing unit is distributed between a downhole processing unit and a processing unit disposed at a surface.

14. The system of claim 10 , wherein the fluid properties of the input parameters comprise a component concentration, an oil density, bubble point pressure and a gas-to-oil ratio, and wherein the component concentration is a lumped component concentration.

15. The system of claim 10 , wherein the iterative parameters further comprise for molecular weight of C6+ components and density of C36+ components of the reservoir fluid.